This section is intended to introduce the reader to various aspects of the art that may be related to various aspects of the present invention. The following discussion is intended to provide information to facilitate a better understanding of the present invention. Accordingly, it should be understood that statements in the following discussion are to be read in this light, and not as admissions of prior art.
Currently, the widely accepted standard to evaluate coronary arteries to assess their degree of stenosis is to perform catheter based x-ray angiography. This offers projective views of the coronary arteries with an in-plane resolution of approximately 0.1×0.1 mm2. Alternative technologies to perform coronary artery imaging include tomographic approaches such as MRI and x-ray Computer Tomography (CT). Currently, CT offers tomographic resolution of approximately 0.5×0.5×0.5 mm3, and MRI offers tomographic resolution of approximately 1×1×1 mm3 Despite the ability to view the coronary arteries with isotropic resolution, both MRI and CT tomographic approaches have been deemed inferior compared to the current catheter based examination. If tomographic resolution were to be improved to match x-ray angiography, CT would have to improve by a factor of 125 and MRI would have to improve by a factor of 1,000. Clearly, these levels of enhancement would require dramatic improvements in performance. The CORE signal preparation approach can be utilized to allow MRI to produce projective angiographic views of the coronary arteries. In this case, to match conventional x-ray angiography the in-plane resolution has to improve by a factor of 100, which requires high efficiency in data collection, but which is more manageable than the original factor of 1,000.
Currently, there is f.o.n.a.r. technique (field focused nuclear magnetic resonance) and sensitive point imaging. In these approaches a signal is preferentially obtained from an approximately spherical region within the body. The FONAR approach of Damadian achieves this by applying static gradients or otherwise warping the main magnetic field, such that signal from outside the point of interest is rapidly dephased, and thus does not contribute a signal. This approach is most suitable for gradient echo imaging. The sensitive point approach of Hinshaw involves application of time varying gradients that dephase signal from outside of the point, and allows the point to be positioned within the body with greater ease than the FONAR approach. Again, the sensitive point method is most compatible with gradient echo imaging. Unlike CORE, neither technique relies on establishing a steady-state signal, they did not envisaged using gradients and RF to excite a cylindrical region, neither technique employed a shaped RF pulse slab-selective region that was progressively rotated, and neither of the existing approaches applied imaging gradients at a fixed orientation as the region of interest was moved.